1. Field of the Invention
This invention concerns a process for producing tantalum concentrates. More particularly, it relates to a process for producing tantalum concentrates from tantalum-containing ores which contain tantalum oxide, tantalic acid or its salts in combination with rutile type titanium dioxide in mixed crystals.
2. Description of the Prior Art
Tantalum containing ores include tantalite, columbite and tantalocolumbite which contain relatively high tantalum content and little or no titanium content, as well as those such as struverite and ilumenorutile which have a relatively low tantalum content and further contain titanium as rutile type titanium dioxide.
Although a process for producing tantalum from the former type ores by using hydrofluoric acid has been known, the process including the use of hydrofluoric acid is unsuitable for the industrial production of tantalum from the latter type ores, since the latter ores have only low tantalum contents and require a great amount of expensive hydrofluoric acid.
In one prior art process for recovering niobium and tantalum values from ores containing metallic impurities such as titanium, the orese are first decomposed with an acid decomposition agent, next a strong reducing agent such as zinc is added to the resultant liquid decomposition product to reduce to soluble compounds and lastly niobium and tantalum values are precipitated from the liquid portion of the reduced decomposition product by hydrolysis (U.S. Pat. No. 2,537,316). In this process, since metallic sulfate is dissolved in the sulfuric acid, it is impossible to recover and reuse the excess sulfuric acid. Therefore, this process is also industrially disadvantageous.
The present inventors have made various studies of the industrial production of tantalum concentrates using ores containing tantalum oxide, tantalic acid or salts thereof in combination with rutile type titanium dioxide in mixed crystals (hereinafter referred to simply as tantalum ores) as the raw ores and, as the result, have discovered that the titanium components contained in the tantalum ores can effectively be dissolved into a diluted sulfuric acid and concentrates containing enriched tantalum concentrates can be obtained as solids, by treating the tantalum ores with concentrated sulfuric acid under specific conditions and reducing the products thus treated in the diluted sulfuric acid.